Ultrasonic surgical instruments are finding increasingly widespread applications in surgical procedures by virtue of the unique performance characteristics of such instruments. Depending upon specific instrument configurations and operational parameters, ultrasonic surgical instruments can provide substantially simultaneous cutting of tissue and homeostasis by coagulation, desirably minimizing patient trauma. The cutting action is typically effected by an end-effector at the distal end of the instrument, which transmits ultrasonic energy to tissue brought into contact with the end-effector. Ultrasonic instruments of this nature can be configured for open surgical use, laparoscopic or endoscopic surgical procedures including robotic-assisted procedures.
Ultrasonic surgical instruments have been developed that include a clamp mechanism to press tissue against the blade of the end-effector in order to couple ultrasonic energy to the tissue of a patient. Such an arrangement (sometimes referred to as a clamp coagulator shears or an ultrasonic transector) is disclosed in U.S. Pat. Nos. 5,322,055; 5,873,873 and 6,325,811. The surgeon activates the clamp arm to press the clamp pad against the blade by squeezing on the handgrip or handle.
Some current designs of clamp coagulator shears utilize a foot pedal to energize the surgical instrument. The surgeon operates the foot pedal while simultaneously applying pressure to the handle to press tissue between the jaw and blade to activate a generator that provides energy that is transmitted to the cutting blade for cutting and coagulating tissue. Key drawbacks with this type of instrument activation include the loss of focus on the surgical field while the surgeon searches for the foot pedal, the foot pedal getting in the way of the surgeon's movement during a procedure and surgeon leg fatigue during long cases.
Various methods have been disclosed for curved end effector balancing, which include repositioning the mass along the end effector. The drawbacks of such methods are i) high stresses in the curved region, which makes the end effector more prone to fracture if it comes in contact with metal during surgery; ii) a shorter active length, which limits the vessel size that can be operated on, (the active length is defined as the length from the distal end of the blade to where the displacement is one half of the displacement at its distal end); and/or iii) the inability to separately balance orthogonal displacements.
Some current designs of clamp coagulator shears utilize handles that are either of a pistol or scissors grips design. The scissor grip designs may have one thumb or finger grip that is immovable and fixed to the housing and one movable thumb or finger grip. This type of grip may not be entirely familiar to surgeons who use other open-type surgical instruments, such as hemostats, where both thumb and finger grips move in opposition to one another. Current designs have scissor arms that rotate around a fixed pivot or rotation point that is perpendicular to the longitudinal axis of the working element. This approach is limited since the relative motion between the two arms is completely rotational. This feature limits the ability to control the pressure profile between the two working ends when fully closed.
Some current designs of clamp coagulator shears are not specifically designed for delicate procedures where precise dissection, cutting and coagulation are required. An exemplary procedure is a thyroidectomy where precise dissection, cutting and coagulation is required to avoid critical blood vessels and nerve bundles.
Some current designs of clamp coagulator shears have an uneven pressure profile across the blade with a higher pressure at the proximal end than the distal end for a given clamp force. An uneven pressure profile can affect the speed and completeness of tissue transaction, especially at the most distal tip of the blade.
Some current designs of clamp coagulator shears incorporate a spring in the handle mechanism to limit the amount of force applied to the blade by the clamp arm. A disadvantage of the spring limiting force mechanism is an increase in pad wear. As the device is used, the pad wears and a groove begins to form in the surface of the pad. This is prevalent in the abuse case where the device is activated when fully closed but with no tissue present between the blade and clamp pad. When the groove becomes deeper, a similar amount of force is placed on the blade due to the spring limit force feature. Therefore, the slope of the force vs. displacement curve is relatively flat.
It would be desirable to provide an ultrasonic surgical instrument that overcomes some of the deficiencies of current instruments. The ultrasonic surgical instrument described herein overcomes those deficiencies.